Physical models of vascular systems are being used extensively in our laboratory to study a variety of hemodynamic phenomena. The projects during the past year are in five major categories: (1) a study of flow in coronary arteries and the influence of arterial stents on the development of turbulence; (2) the application of diastolically-phased, high velocity pulsed injections to reduce streaming during intracarotid administration of BCNU solutions for treating brain tumors; (3) a study comparing effects on vascular patency and hemolysis of blood withdrawal by vacutainers, versus a manual syringe method; (4) a study of flow around a sphere concentric to a tube as an idealized model of a balloon catheter in a vessel; and (5) an investigation of the streaming of pancreatic gastrin secretions due to the stable flow field at the confluence of the superior mesenteric and splenic veins into the portal vein.